I.C. cards are known that are usable in banking and also for prepayment purposes: e.g. prepayment of a telephone call, prepayment of parking time for a vehicle, etc. Such I.C. cards normally include a card body made of plastic in which a cavity is formed, which cavity receives an electronics micromodule provided with contact metallization for providing electrical communication between the micromodule and the outside world. I.C. cards have also been envisaged in which the micromodule is not provided with contact metallization. In such applications, communication with the card takes place by radio.
One of the problems encountered with I.C. cards is their mechanical strength. To this end, in order to be acceptable for use by the general public, cards must be capable of passing severe stress testing. During such testing which simulates situations that may arise in use, a card is curved some number of times perpendicularly to its long axis or to its short axis. A card is considered as passing such a test if the micromodule has not become detached after a series of curving operations has been completed, and/or if the stresses have not been transferred to the micromodule sufficiently to break it. Other tests relate to the bending strength of card bodies. In such tests, manufactured cards are required to withstand as high a bending force as possible. Beneath a given bending force card bodies are rejected, above it they are accepted.
For the reasons mentioned above, card bodies have thus been reinforced, either overall or else in the proximity of the region in a card body having the cavity which receives the micromodule. For example, European patent application number 0 071 255 published on Feb. 9, 1983 describes I.C. card media in which the plastic material used for the card body medium is reinforced with glass fibers. In such a configuration, during co-lamination of the layers of the card body, use is made of a co-lamination core constituted by epoxy resin reinforced with glass fibers.
In magnetic track card applications, the back of a card is covered with a magnetic track in which information is recorded. A reader can receive such cards and decode the information recorded thereon for the purpose of identifying the card bearer. Normally the density of information actually stored on such tracks is low so as to provide tolerance to large variations in use. The difference between magnetic track cards and I.C. cards comes from the fact that the quantity of information that can be stored with magnetic tracks is greater than the quantity that can be stored with electronic micro modules, but that access to the information is slower with magnetic tracks than it is with micromodules. In contrast, from the security point of view, magnetic track cards provide no security guarantee at all. Very rudimentary equipment is all that is required for duplicating the information from such cards to cards made unprofessionally, thereby enabling cards to be used in ways that were not intended when they were issued. There also exist combined cards having both electronic and magnetic memory. The purpose is to make best use of the performance available from each of the two types of memory media. At present, practical use of such cards is prevented by problems associated with different tolerances in use.
It has also been observed that problems of dimensional stability occur because of the range of temperatures to which cards are subjected in use. Dual memory type cards, in particular, can only be made both long-lasting and highly reliable if they are simultaneously of great dimensional stability and also of considerable mechanical stiffness. In addition, making the card body of plastic gives rise to considerable electrostatic discharge phenomena which are injurious both to an electronic micromodule and to a magnetic track.
An object of the invention is to remedy the above-mentioned drawbacks by proposing a technique for reinforcing cards that leads to such mechanical stability independently of temperature and which adapts itself to the mechanical and/or thermal expansion behavior of the micromodule or of the magnetic track. Thermal expansion can change a magnetic track to such an extent that the resulting format thereon no longer lies within the standards laid down. In order to adapt the deformation effects so as to keep them within a range of tolerances that is compatible with both of the technologies and regardless of temperature, the card body is reinforced in accordance with the invention by using at least two sheets of different strengthening materials. Each of these sheets is organized in a matrix configuration and the two matrix configurations are preferably intermeshed, e.g. by offsetting one of the sheets by half a pitch relative to the other. It is then observed that the card body made of plastic itself absorbs the differential forces due to the two different materials, and instead of this leading to the card breaking up, it leads on the contrary to tolerances being satisfied accurately.